CERN Courier January/February 2017 CERN Courier January/February 2017 Antimatter and gravity Supergravity at 40 H and H+ antihydrogen atoms to interact with a beam of photons, promising a sensitivity in the 10–6 range. porous target Ps e+ porous target The many lives of Cooling matter e+ Ps double laser pulse In the case of AEgIS, the defl ectometer principle that underpins accelerating laser pulse the measurement has already been demonstrated with matter Ps* electric field atoms and with antiprotons, while the time-of-fl ight measure- p ment is straightforward in the case of GBAR. The diffi culty for supergravity p H beam the experiments lies in preparing suffi cient numbers of antiatoms p + Ps → H + e– * * – at the required low velocities. ALPHA has already demonstrated p + Ps → H + e + – H + Ps → H + e trapping of several hundred antiatoms at a temperature below The production of antihydrogen in AEgIS (left) and GBAR (right) 0.5 K, corresponding to random velocities of the order 10 m/s. The is performed via the interaction of antiprotons with positronium antiatoms are formed by letting the antiprotons traverse a plasma (Ps). In AEgIS, a plasma of antiprotons at rest in a Penning trap of positrons located within the same Penning trap. is showered with excited positronium atoms, producing excited A different scheme is used in AEgIS and GBAR to form and antihydrogen atoms that are accelerated to form a beam. In possibly cool the antiatoms and anti-ions. In AEgIS, antiprotons GBAR, a dense positronium cloud is traversed by a beam of are cooled within a Penning trap and receive a shower of positro- antiprotons to produce antihydrogen atoms and ions. nium atoms (bound e+e– pairs) to form the antiatoms. These are then slightly accelerated by electric fi elds (which act on the atoms’ to test such quantum effects. Any difference would probably not induced electric-dipole moments) so that they exit the charged change anything in the observable universe, but it would point to particle trap axially in the form of a neutral beam. For GBAR, the the necessity of having a quantum theory of gravity. antiproton beam traverses a cloud of positronium to form the anti- AEgIS plans to measure the vertical deviation of a pulsed hori- ions, which are then cooled to a few μK by forcing them to interact zontal beam of cold antihydrogen atoms, generated by bringing with laser-cooled beryllium ions. laser-excited positronium moving at several km/s into contact with In this race towards low energies, ALPHA and AEgIS are located cold antiprotons, travelling with a velocity of a few hundred m/s. on the beam at the AD, which delivers 5 MeV antiprotons. While The resulting highly excited antihydrogen atoms are then acceler- AEgIS is already commissioning its dedicated gravity experiment, ated horizontally and a moiré defl ectometer used to measure the ALPHA will move from spectroscopy to gravity in the coming vertical deviation, which is expected to be a few microns given the months. GBAR, which will be the fi rst experiment to make use of approximately 1 m-long fl ight tube of AEgIS. Reaching the lowest the beam delivered by ELENA, is now beginning installation and possible antiproton temperature minimises the divergence of the expects fi rst attempts at anti-ion production in 2018. ELENA will beam and therefore maximises the fl ux of antihydrogen atoms that decelerate antiprotons coming from the AD from 5 MeV to just Forty years after theorists married general In the early 1970s, grand unifi ed theories (GUTs), based on larger end up on the downstream detector. 100 keV, making it more effi cient to trap and store antimatter. Fol- gauge symmetries that include the SM’s “SU(3) × SU(2) × U(1)” In GBAR, which takes advantage of advances in ion-cooling lowing commissioning fi rst with protons and then with hydrogen relativity with supersymmetry, supergravity structure, did unify colour and charge – thereby uniting the strong – techniques, antihydrogen ions (H+) are produced with veloci- ions, ELENA should receive its fi rst antiprotons in the middle of and electroweak interactions. However, they relied on a huge new continues to carve out new directions in the 16 ties of the order of 0.5 m/s. In a second step, the anti-ions will be 2017 (CERN Courier December 2016 p16). Along with precision energy scale (~10 GeV), just a few orders of magnitude below the stripped of one positron to give an ultra-slow neutral antiatom that tests of CPT invariance, this facility will help to ensure that any search for a unifi ed theory. Planck scale of gravity (~1019 GeV) and far above the electroweak is allowed to enter free fall. The time of free fall over a height of differences in the gravitational antics of antimatter are not missed. Fermi scale (~10 2 GeV), and on new particles carrying both colour 20 cm is as long as 200 ms, which is easily measurable. These num- and electroweak charges. As a result, GUTs made the stunning pre- bers cor respond to the gravitational acceleration known for matter Résumé The early 1970s was a pivotal period in the history of particle phys- diction that the proton might decay at detectable rates, which was atoms, and the expected sensitivity to small deviations is 1% in the L’antimatière tombe-t-elle vers le haut ? ics. Following the discovery of asymptotic freedom and the Brout– eventually excluded by underground experiments, and their two fi rst phase of operation. Englert–Higgs mechanism a few years earlier, it was the time when widely separated cut-off scales introduced a “hierarchy problem” The ALPHA-g experiment will release antihydrogen atoms Le principe d’équivalence est au centre de la théorie de la relativité the Standard Model (SM) of electroweak and strong interactions that called for some kind of stabilisation mechanism. from a vertical magnetic atom trap and record their positions générale ; selon ce principe, testé avec une précision toujours plus came into being. After decades of empirical verifi cation, the theory A possible solution came from a parallel but unrelated devel- when they annihilate on the walls of the experiment. In a proof- fi ne au cours des dernières décennies, toute la matière tombe à received a fi nal spectacular confi rmation with the discovery of the opment. In 1973, Julius Wess and Bruno Zumino unveiled a new of-principle experiment using the original ALPHA atom trap, the la même vitesse. Trois collaborations (ALPHA, AEgIS et GBAR) Higgs boson at CERN in 2012, and its formulation has also been symmetry of 4D quantum fi eld theory: supersymmetry, which acceleration of antihydrogen atoms by gravity was constrained préparent actuellement des expériences auprès du Décélérateur recognised by Nobel prizes awarded to theoretical physics in 1979, interchanges bosons and fermions and, as would be better appreci- to lie anywhere between –110 g and 65 g. ALPHA-g improves d’antiprotons du CERN afi n de vérifi er si ce principe est valable 1999, 2004 and 2013. ated later, can also conspire to stabilise scale hierarchies. Super- on this original demonstration by orienting the trap vertically, également pour l’antimatière, en mesurant la manière dont It was clear from the start, however, that the SM, a spontaneously symmetry was inspired by “dual resonance models”, an early thereby enabling better control of the antiatom release and les atomes d’antihydrogène tombent sous l’effet de la gravité. broken gauge theory, had two major shortcomings. First, it is not version of string theory pioneered by Gabriele Veneziano and improving sensitivity to the vertical annihilation position. In the Toute différence par rapport à des atomes d’hydrogène normal a truly unifi ed theory because the gluons of the strong (colour) extended by André Neveu, Pierre Ramond and John Schwarz. Ear- new arrangement, antihydrogen gravitation can be measured at suggérerait que des effets quantiques entrent en ligne de compte ; force and the photons of electromagnetism do not emerge from a lier work done in France by Jean-Loup Gervais and Benji Sakita, the 10% level, which would already settle the question of whether nous aurions alors besoin d’une théorie quantique de la gravité. common symmetry. Second, it leaves aside gravity, the other fun- and in the Soviet Union by Yuri Golfand and Evgeny Likhtman, antimatter falls up or down, but improvements in cooling tech- damental force of nature, which is based on the gauge principle of and by Dmitry Volkov and Vladimir Akulov, had anticipated some niques will allow measurements at the 1% level. A long-term Patrice Perez, CEA-Irfu Saclay, Michael Doser, CERN, and general co-ordinate transformations and is described by general of supersymmetry’s salient features. ▲ aspiration of the ALPHA-g project is to use techniques that cause William Bertsche, University of Manchester. relativity (GR). An exact supersymmetry would require the existence of 40 41 CERNCOURIER www. V OLUME 5 7 N UMBER 1 J AARYN U /F EBRUARY 2 0 1 7 CERN Courier January/February 2017 CERN Courier January/February 2017 Supergravity at 40 Supergravity at 40 fi eld of supersymmetry, just like the photon is the gauge fi eld of internal circle rotations. If one or more local supersymmetries electromagnetic N helicity content electroweak 3 (whose number will be denoted by N) accompany general co- 1 [(2), ( 2 ( ] ordinate transformations, they grant the consistency of gravitino weak GUTs ? 2 3 interactions. In a subclass of “pure” supergravity models, super- [(2), 2 ( 2 ( , (1)] strong symmetry also allows one to connect “marble” and “wood” and 3 1 3 [(2), 3 ( 2 ( , 3(1), ( 2 ( ] therefore goes well beyond the KK mechanism, which does not supersymmetry? SSMs ? SUSY GUTs ? 4 [(2), 4 ( 3 ( , 6(1), 4( 1 ( , 2(0)] link Bose and Fermi fi elds.